Image capturing and correction apparatus, image capturing and correction method, and medium storing a program

ABSTRACT

Provided is an image processing apparatus comprising a region identifying section that identifies a partial region that fulfills a preset condition in a main image captured through an optical system in which an optical transfer function relating to light from an object point is substantially uniform regardless of a distance to the object point; and a correcting section that corrects an image of the partial region identified by the region identifying section, according to the optical transfer function of the optical system. The image processing apparatus may further comprise a condition storing section that stores the condition to be fulfilled by the partial region corrected by the correcting section, and the region identifying section may identify a partial region of the main image that fulfills the condition stored by the condition storing section.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese PatentApplications No. 2008-025709 filed on Feb. 5, 2008 and No. 2009-007991filed on Jan. 16, 2009, the contents of which are incorporated herein byreference.

BACKGROUND

1. Technical Field

The present invention relates to an image processing apparatus, an imageprocessing method, and a program. In particular, the present inventionrelates to an image processing apparatus and an image processing methodfor processing an image, and a computer readable medium storing thereona program used by image processing apparatus.

2. Description of the Related Art

A camera provided with an objective lens having a PSF two times greaterthan the pitch of the light receiving element array is known as in, forexample, Japanese Unexamined Patent Application Publication No.2006-519527. Furthermore, an electronic camera that can easily capturequality images by switching between image capturing and image processingaccording to a selected image capturing mode is known as in, forexample, Japanese Patent Application Publication No. 2001-311867.

The invention disclosed in JP 2006-519527 restores an entire image, butuses a process having a very high computational cost. Furthermore, adifference arises in the OTF between objects that are at very differentdistances, and may also arise between an object on the optical axis andan object off of the optical axis. Accordingly, when performing the samerestoration process for all of the image regions, there is a problemthat artifacts are generated. JP 2001-311867 does not disclose acorrection method using the optical transfer function.

SUMMARY

Therefore, it is an object of an aspect of the innovations herein toprovide an image capturing apparatus, an image capturing method and acomputer readable medium which are capable of overcoming the abovedrawbacks accompanying the related art. The above and other objects canbe achieved by combinations described in the independent claims. Thedependent claims define further advantageous and exemplary combinationsof the innovations herein.

According to the first aspect related to the innovations herein, oneexemplary image processing apparatus comprises a region identifyingsection that identifies a partial region that fulfills a presetcondition in a main image captured through an optical system in which anoptical transfer function relating to light from an object point issubstantially uniform regardless of a distance to the object point; anda correcting section that corrects an image of the partial regionidentified by the region identifying section, according to the opticaltransfer function of the optical system.

According to the second aspect related to the innovations herein, oneexemplary image processing method comprises identifying a partial regionthat fulfills a preset condition in a main image captured through anoptical system in which an optical transfer function relating to lightfrom an object point is substantially uniform regardless of a distanceto the object point; and correcting an image of the identified partialregion according to the optical transfer function of the optical system.

According to the third aspect related to the innovations herein, oneexemplary storage medium may include computer readable medium storingthereon a program used by an image processing apparatus, the programcausing a computer to function as a region identifying section thatidentifies a partial region that fulfills a preset condition in a mainimage captured through an optical system in which an optical transferfunction relating to light from an object point is substantially uniformregardless of a distance to the object point; and a correcting sectionthat corrects an image of the partial region identified by the regionidentifying section, according to the optical transfer function of theoptical system.

According to the fourth aspect related to the innovations herein, oneexemplary image processing apparatus comprises a correcting section thatcorrects an image captured through an optical system in which an opticaltransfer function relating to light from an object point issubstantially uniform regardless of a distance to the object point,according to the optical transfer function of the optical system; aregion identifying section that identifies, in the image corrected bythe correcting section, an overcorrected partial region in which anoptical response of the optical system is overcorrected; and acorrection control section that suppresses intensity of the correctionby the correcting section in the overcorrected partial region identifiedby the region identifying section.

According to the fifth aspect related to the innovations herein, oneexemplary image processing method comprises correcting an image capturedthrough an optical system in which an optical transfer function relatingto light from an object point is substantially uniform regardless of adistance to the object point, according to the optical transfer functionof the optical system; identifying, in the corrected image, anovercorrected partial region in which an optical response of the opticalsystem is overcorrected; and controlling intensity of the correction inthe identified overcorrected partial region.

According to the sixth aspect related to the innovations herein, oneexemplary storage medium may include a computer readable medium storingthereon a program used by an image processing apparatus, the programcausing a computer to function as a correcting section that corrects animage captured through an optical system in which an optical transferfunction relating to light from an object point is substantially uniformregardless of a distance to the object point, according to the opticaltransfer function of the optical system; a region identifying sectionthat identifies, in the image corrected by the correcting section, anovercorrected partial region in which an optical response of the opticalsystem is overcorrected; and a correction control section thatsuppresses intensity of the correction by the correcting section in theovercorrected partial region identified by the region identifyingsection.

The summary clause does not necessarily describe all necessary featuresof the embodiments of the present invention. The present invention mayalso be a sub-combination of the features described above. The above andother features and advantages of the present invention will become moreapparent from the following description of the embodiments taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary block configuration of an imagecapturing apparatus 100 relating to an embodiment of the presentinvention.

FIG. 2 schematically illustrates exemplary optical characteristics of alens system 110.

FIG. 3 illustrates an exemplary configuration of the lens system 110.

FIG. 4 illustrates aberration characteristics of the lens system 110shown in FIG. 3.

FIG. 5 illustrates optical transfer characteristics of the lens system110 shown in FIG. 3.

FIG. 6 illustrates exemplary arrangement of light receiving elementsincluded in a light receiving section 120.

FIG. 7 illustrates an exemplary block configuration of a non-linearprocessing section 170.

FIG. 8 illustrates exemplary data stored on a condition storing section180 by using a table.

FIG. 9 illustrates exemplary partial regions identified by a regionidentifying section 160.

FIG. 10 illustrates diffraction limited MTF of the lens system 110.

FIG. 11 illustrates MTF characteristics corrected by the correctingsection 140.

FIG. 12 shows an example of a plurality of image regions in a finalimage.

FIG. 13 schematically shows an example of distance ranges indicatingpositions where a subject exists whose image can be corrected.

FIG. 14 shows an exemplary table of information stored by the conditionstoring section 180 and the parameter storing section 185.

FIG. 15 shows examples of spatial frequency dependencies of MTFs.

FIG. 16 shows an exemplary captured image.

FIG. 17 shows a positional relation between the image capturingapparatus 100 and the subjects.

FIG. 18 illustrates an exemplary hardware configuration of a computer1500 functioning as the image capturing apparatus 100.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Some aspects of the invention will now be described based on theembodiments, which do not intend to limit the scope of the presentinvention, but exemplify the invention. All of the features and thecombinations thereof described in the embodiment are not necessarilyessential to the invention.

FIG. 1 illustrates an exemplary block configuration of an imagecapturing apparatus 100 relating to an embodiment of the presentinvention. The image capturing apparatus 100 image-captures a subjectand generates an image. The image capturing apparatus 100 includes alens system 110, a light receiving section 120, an A/D convertingsection 125, a linear processing section 130, a correcting section 140,a non-linear processing section 170, an output section 150, a regionidentifying section 160, a distance obtaining section 165, a conditionstoring section 180, a parameter storing section 185, and a correctioncontrol section 175. The lens system 110 exemplifies an optical systemthat focuses light, and the light receiving section 120 receives lightthat has passed through the lens system 110.

The lens system 110 achieves substantially the same optical transferfunction for light from an object point, irrespective of the distancebetween the object point and the lens system 110. The opticalcharacteristics of the lens system 110 are qualitatively described withreference to FIG. 2.

The light receiving section 120 includes a plurality of light receivingelements arranged two-dimensionally. The light receiving elementsreceive light from a subject that is focused by the lens system 110. TheA/D converting section 125 A/D converts a signal indicative of theamount of the light received by each of the light receiving elements andsupplies a digital pixel value that is linearly related to the amount ofthe received light to the linear processing section 130. The linearprocessing section 130 processes the pixel value while maintaining thelinear relation of the pixel value to the amount of the received light.The processes performed by the linear processing section 130 mayinclude, for example, darkness correction and defective pixelcorrection. The pixel value processed by the linear processing section130 is supplied to the region identifying section 160, the correctingsection 140 and the non-linear processing section 170.

The correcting section 140 corrects an image represented by the pixelvalues supplied from the linear processing section 130. For example, thecorrecting section 140 uses a plurality of pixel values supplied fromthe A/D converting section 125 and the optical transfer function of thelens system 110 in order to correct an image represented by theplurality of pixel values. In this way, the correcting section 140corrects a plurality of pixel values that are linearly related to theamounts of light received the respective light receiving elements,according to the optical transfer function of the lens system 110.

The non-linear processing section 170 performs image processing on theimage that has been corrected by the correcting section 140. The imageprocessing operations performed by the non-linear processing section 170may include, for example, a color balance operation, a γ correctionoperation, a coinciding operation, a contour correcting operation, and acolor correcting operation. In this way, the non-linear processingsection 170 converts a plurality of pixel values that have beencorrected by the correcting section 140 into pixel values that arenon-linearly related to the amounts of the light received by therespective light receiving elements.

As described above, the non-linear processing section 170 converts thepixel values representing the image that has been corrected by thecorrecting section 140 into values that are non-linearly related to theamounts of the light received by the light receiving elements. In otherwords, the correcting section 140 corrects an image according to theoptical transfer function before the non-linear processing section 170performs any operations. Therefore, the image capturing apparatus 100can correctly restore an image of a subject.

The output section 150 outputs an output image that is obtained as aresult of the operations performed by the correcting section 140 and thenon-linear processing section 170. For example, the output section 150may display the output image. As an alternative example, the outputsection 150 may record the output image onto a recording medium. As afurther alternative example, the output section 150 may transmit theoutput image to a communication link. Here, the output section 150 mayfirst compress the output image and then output the compressed image.

The region identifying section 160 identifies a partial regionsatisfying a predetermined condition in an image captured through thelens system 110. Specifically speaking, the condition storing section180 stores a condition to be satisfied by a partial region that is to becorrected by the correcting section 140. The region identifying section160 identifies, in an image, a partial region satisfying the conditionstored on the condition storing section 180. The correcting section 140then corrects an image shown by the partial region identified by theregion identifying section 160, according to the optical transferfunction of the lens system 110.

For example, the condition storing section 180 stores a conditionrelated to a distance from the lens system 110 to a subject.Specifically speaking, the condition storing section 180 stores such arange for the distance from the lens system 110 to an object point thatthe lens system 110 has substantially the same optical transfer functionfor light from the object point. The region identifying section 160identifies a partial region showing a subject that is located at adistance that falls within the distance range stored on the conditionstoring section 180. For example, the distance obtaining section 165obtains the distance from the lens system 110 to an image-capturedsubject. The region identifying section 160 identifies a partial regionshowing a subject that is located at a distance, which is obtained bythe distance obtaining section 165, that falls within the distance rangestored on the condition storing section 180. In this manner, the regionidentifying section 160 identifies a partial region showing a subjectthat is located at a distance that satisfies the condition stored on thecondition storing section 180.

As a different example, the condition storing section 180 may store acondition relating to brightness of an image obtained by irradiating asubject with illumination light, where the subject is located at adistance that falls within such a range of the distance from the lenssystem 110 to the object point that the lens system 110 hassubstantially the same optical transfer function for light from theobject point. In this case, the region identifying section 160 mayidentify, in an image showing a subject irradiated with illuminationlight, a partial region with brightness satisfying the conditionrelating to brightness which is stored on the condition storing section180.

As a further different example, the condition storing section 180 maystore a condition relating to a type of a subject. In this case, theregion identifying section 160 may identify a partial region showing asubject the type of which satisfies the condition relating to a type ofa subject which is stored on the condition storing section 180. As afurther different example, the condition storing section 180 may store acondition relating to a color of a subject. In this case, the regionidentifying section 160 may identify a partial region showing a subjectsatisfying the condition relating to a color of a subject which isstored on the condition storing section 180.

The region identifying section 160 identifies an overcorrected partialregion in the image that has been corrected by the correcting section140. Here, the overcorrected partial region indicates a partial regionin which the optical response of the lens system 110 is overcorrected.Specifically speaking, the region identifying section 160 identifies, inthe image that has been corrected by the correcting section 140, anovercorrected partial region, which is a partial region including afrequency range in which the optical response of the lens system 110 iscorrected by more than a predetermined value. The correction controlsection 175 controls the intensity of the correction by the correctingsection 140 in the overcorrected partial region identified by the regionidentifying section 160. With such a configuration, the image capturingapparatus 100 can prevent an image output by the output section 150 fromincluding an artifact.

The parameter storing section 185 stores, in association with each of aplurality of different distance ranges, a correction parametercorresponding to the optical transfer function across the distancerange. The correcting section 140 corrects the image of each partialregion identified by the region identifying section 160 using thecorrection parameter stored in the parameter storing section inassociation with the distance range of the subject captured in thepartial region.

The A/D converting section 125, the linear processing section 130, thecorrecting section 140, the non-linear processing section 170, theoutput section 150, the region identifying section 160, the distanceobtaining section 165, the condition storing section 180, and thecorrection control section 175 can implement an image processingapparatus.

FIG. 2 schematically illustrates exemplary optical characteristics ofthe lens system 110. FIG. 2 schematically shows the paths of a light ray210, a light ray 220 and a light ray 230 that are incident on anentrance pupil 205 at different positions from an optical axis 200.Here, the light rays 210, 220 and 230 are some of the light rays thatare incident on the lens system 110 from an object point on the opticalaxis 200. As shown in FIG. 2, the incident positions on the entrancepupil 205 of the light rays 210, 220 and 230 become more distant fromthe optical axis 200 in the stated order.

As shown in FIG. 2, with the help of the lens system 110, the light ray210 crosses over the optical axis 200 at a position 215. The position215 is positioned away from a position 250 of a paraxial focus in thedirection of the optical axis 200 so as to be on the opposite side ofthe lens system 110. Also, with the help of the lens system 110, thelight ray 230, which is incident at the most distant position from theoptical axis 200, crosses over the optical axis 200 at a position 235.The position 235 is positioned away from the position 215 in thedirection of the optical axis 200 so as to be on the opposite side ofthe lens system 110. With the help of the lens system 110, the light ray220 crosses over the optical axis 200 at a position 225 that is betweenthe positions 215 and 235.

As shown in FIG. 2, spread of light caused by the lens system 110 isexpected to have substantially the same size within an interval betweenthe position 215 and the position 235. Thus, the lens system 110 hasovercorrected spherical aberration and focuses light at a positionsubstantially further than the position 250 of the paraxial focus.Accordingly, the lens system 110 can increase an interval in the opticalaxis direction within which light from an object point has spread ofsubstantially the same size irrespective of an image plane position inthe optical axis direction, when compared with the case where thespherical aberration is not overcorrected.

Such an increase in the interval in the optical axis direction resultsin an increase in the range for the distance between the lens system 110and such an object point that light from the object point has spread ofsubstantially the same size. For the widened range, one image planeposition can be determined. By disposing the light receiving section 120at such an image plane position, substantially the same optical transferfunction is achieved at the position of the light receiving section 120irrespective of the distance between the object point and the lenssystem 110. In this way, the above-described aberration characteristicsof the lens system 110 can achieve substantially the same opticaltransfer function for light from an object point irrespective of thedistance between the object point and the lens system 110.

In the above, the optical characteristics of the lens system 110 arequalitatively described with reference to FIG. 2. Here, note that theschematic illustration of the lens system 110 shown in FIG. 2 isprovided only in order to qualitatively explain the opticalcharacteristics of the lens system 110 and does not reflect the realdimensions.

FIG. 3 illustrates an exemplary configuration of the lens system 110.The lens system 110 includes a diaphragm 700, a lens 710, a lens 720,and a lens 730. A reference numeral 780 designates an image plane. InFIG. 3, a plurality of light rays overlap the lens system 110. Thefollowing explains the arrangement and optical characteristics of thelenses 710, 720 and 730.

The refractive index of the lenses 710 and 730 takes values of1.53128710, 1.52470166 and 1.52196091 for light having wavelengths of486.133 nm, 587.562 nm and 656.273 nm. The refractive index of the lens720 takes values of 1.59943869, 1.58546992, and 1.57986377 for lighthaving wavelengths of 486.133 nm, 587.562 nm, and 656.273 nm. Thediaphragm 700 is spaced away from the vertex of the lens 710 by adistance of 0.001566661 mm so as to be positioned between the vertex ofthe lens 710 and the image plane.

The lens 710 has a thickness of 1.987091 mm. In the explanation of FIG.3, the term “thickness” denotes the length of a lens in the optical axisdirection. Referring to a surface of the lens 710 that faces an object,the radius of curvature is 15.48676 mm, the radius of the cross sectionis 1.188941 mm, and the conical constant is −90378.4. Referring to asurface of the lens 710 that faces an image, the radius of curvature is−12.09038 mm, the radius of the cross section is 2.14803 mm, and theconical constant is 28.79374. In the explanation of FIG. 3, when asurface has a negative radius of curvature, the surface is shaped as aconcave surface for light.

The lens 720 is spaced away from the lens 710 by a distance of 0.4005282mm so as to be positioned between the lens 710 and the image plane. Inthe explanation of FIG. 3, a distance between lenses denotes a distance,on an optical axis, between an image-plane-side surface of one of thelenses that is closer to an object and an object-side surface of theother lens that is closer to an image plane. The lens 720 has athickness of 0.09214797 mm. Referring to a surface of the lens 720 thatfaces the object, the radius of curvature is 2.114035 mm, the radius ofcross section is 2.38122 mm, and the conical constant is −0.3929276.Referring to a surface of the lens 720 that faces the image, the radiusof curvature is 1.119414 mm, the radius of cross section is 2.362124 mm,and the conical constant is −2.780465.

The lens 730 is spaced away from the lens 720 by a distance of 1.770789mm so as to be positioned between the lens 720 and the image plane. Thelens 730 has a thickness of 0.5204438 mm. Referring to a surface of thelens 730 that faces the object, the radius of curvature is −0.6002893mm, the radius of cross section is 3.486572 mm, and the conical constantis −958.9289. Referring to a surface of the lens 730 that faces theimage, the radius of curvature is −0.3018179 mm, the radius of crosssection is 4.262504 mm, and the conical constant is −465.3071. The imageplane is positioned away from the lens 730 by a distance of 1.1 mm.

As stated above, the lenses 710, 720 and 730 are coaxially arranged withtheir central axes being aligned to each other. Therefore, the lenssystem 110 is rotationally symmetrical with respect to the optical axis.

The absolute value of the difference between the angle of the normal ofthe image plane and the angle at which a main light ray is incident onthe image plane is set smaller than a predetermined value so that acalculation error of the optical transfer function of the lens system110 is made smaller than a predetermined value. As stated, thecalculation error of the optical transfer function can be reduced byincreasing the telecentric characteristics of the lens system 110. Forexample, an MTF can be calculated with a sufficiently small error bymeans of FFT. Therefore, the image capturing apparatus 100 can restoreat a high speed an image that is blurred by the lens system 110.

FIG. 4 illustrates the aberration characteristics of the lens system 110shown in FIG. 3. FIG. 4 includes, beginning at the top, a diagramshowing the spherical aberration, diagrams showing the astigmatism andthe distortion aberration, and diagrams showing the transverseaberration. As seen from the top drawing showing the sphericalaberration, the spherical aberration of the lens system 110 shown inFIG. 3 is overcorrected. In this diagram showing the sphericalaberration, the horizontal axis represents a position relative to adefined image plane, not a position relative to a paraxial focus.

As seen from the diagram, the longitudinal aberration takes positivevalues across the entire image plane. In other words, the longitudinalaberration takes positive values at least for light that is incident onthe entrance pupil of the lens system 110 at a position that fallswithin a range between a first incident position and the optical axis,where the first incident position is spaced away from the optical axisby a first distance.

At the bottom, FIG. 4 has diagrams showing the transverse aberration inassociation with a plurality of image heights. The upper left diagramshows the transverse aberration on the optical axis, the upper rightdiagram shows the transverse aberration at an image height of 14.10 mm,the lower left diagram shows the transverse aberration at an imageheight of 19.74 mm, and the lower right diagram shows the transverseaberration at an image height of 28.20 mm. As seen from these diagrams,the transverse aberration of the lens system 110 is shaped insubstantially the same manner for each of the image heights.

FIG. 5 illustrates the optical transfer characteristics of the lenssystem 110 shown in FIG. 3. FIG. 5 includes, beginning at the top, adiagram showing how spot diagrams are dependent on image heights anddefocus amounts, a diagram showing how the MTF is dependent on defocusamounts, and a diagram showing spatial frequency characteristics of theMTF.

The top drawing shows spot diagrams obtained for different image heightsand different defocus amounts. In this diagram, a plurality of spotdiagrams for the same image height and for different defocus amounts arearranged next to each other in the horizontal direction. Also, aplurality of spot diagrams for the same defocus amount and for differentimage heights are arranged next to each other in the vertical direction.

Numerical values written on the left side of the spot diagrams denoteimage heights. As indicated by these numerical values, the top drawingincludes spot diagrams obtained with the image height from the opticalaxis being set to zero (i.e., on the optical axis), 14.10 mm, 19.74 mm,and 20.20 mm. Numerical values written under the spot diagrams denotedefocus amounts. As indicated by these numerical values, the top drawingincludes spot diagrams obtained at a position spaced away from a definedimage plane by −75 μm, at a position spaced away from the image plane by−37.5 μm, at a position of the image plane, at a position spaced awayfrom the image plane by 37.5 μm, and at a position spaced away from theimage plane by 75 μm.

The top drawing in FIG. 5 indicates that the spot diagrams havesubstantially the same spread for image planes differently positioned inthe optical axis direction at least within a predetermined range,irrespective of the image heights. Thus, spread of light from an objectpoint caused by the lens system 110 is substantially the same at imageplane positions that are different from each other in the optical axisdirection within a predetermined range. Here, spread of light may denotespread of a spot diagram as referred to in FIG. 5 or spread of lightrepresented by a point image distribution function. As described above,spread of light from an object point caused by the lens system 110 issubstantially the same irrespective of the image heights, and spread oflight from an object point caused by the lens system 110 issubstantially the same at image plane positions different from eachother in the optical axis direction at least within a predeterminedrange.

As seen from the middle diagram showing how the MTF is dependent ondefocus amounts, substantially the same MTF value distributions areobtained for different image heights irrespective of whether a light rayis a sagittal ray or meridional ray. The MTF takes substantially thesame value at least within a certain range of defocus amounts that isshown in FIG. 5. In this way, the MTF of the lens system 110 takessubstantially the same value for a wide range of defocus amounts.

As seen from the bottom diagram showing the spatial frequencycharacteristic of the MTF, the lens system 110 has substantially thesame MTF-frequency characteristics for different image heights,irrespective of whether a light ray is a sagittal ray or meridional ray.In other words, the MTF of the lens system 110 is substantially the sameirrespective of the image heights. Furthermore, the MTF of the lenssystem 110 is substantially the same across image plane positionsdifferent from each other in the optical axis direction within apredetermined range. As described above, the lens system 110 spreadslight from an object point to have substantially the same size at thelight receiving section 120 irrespective of the distance between theobject point and the lens system 110, so that the lens system 110 hassubstantially the same optical transfer function for light from anobject point irrespective of the distance between the object point andthe lens system 110.

FIG. 6 illustrates exemplary arrangement of the light receiving elementsincluded in the light receiving section 120. The light receiving section120 includes a light receiving element unit 650 a constituted by lightreceiving elements 610 a and 610 b receiving light of the G component, alight receiving element 620 receiving light of the R component, and alight receiving element 630 receiving light of the B component. Thelight receiving section 120 is formed by two-dimensionally arranging aplurality of light receiving element units each of which has lightreceiving elements arranged in the same manner as in the light receivingelement unit 650 a, for example, a light receiving element unit 650 bconstituted by light receiving elements 611 a and 611 b receiving lightof the G component, a light receiving element 621 receiving light of theR component, and a light receiving element 631 receiving light of the Bcomponent.

As described above, the light receiving section 120 has a plurality oflight receiving elements each of which is configured to receive light ofone of a plurality of color components. The light receiving elementsform a substantially planar light receiving surface in the lightreceiving section 120. The light receiving surface of the lightreceiving section 120 is set substantially perpendicular to the opticalaxis of the lens system 110. Here, the light receiving elements may beCCD or MOS imaging elements.

Here, spread of light from an object point caused by the lens system 110is set to be larger than the pitch of the light receiving elementsincluded in the light receiving section 120, at a position of the lightreceiving section 120. The pitch of the light receiving elements hereindenotes the pitch of light receiving elements configured to receivelight in a wavelength range representing the same color component. Forexample, the pitch of the light receiving elements may denote thedistance between the position of the light receiving element 620 and theposition of the light receiving element 621. Therefore, the lens system110 spreads light from an object point so that two or more of the lightreceiving elements receive the light.

In this case, light from an object point is received by the lightreceiving elements after passing through the lens system 110. Therefore,an image of a subject becomes blurry. If the optical transfer functionof the lens system 110 is known, however, the image of the subject canbe restored with the help of image processing designed for correctingthe spread caused by the lens system 110, which is implied by theoptical transfer function.

For example, it is assumed that spread of light from an object pointcaused by the lens system 110 covers a predetermined number of lightreceiving elements at the position of the light receiving section 120.In this case, the correcting section 140 can correct an image based onthe amounts of light received by the predetermined number of lightreceiving elements and the optical transfer function of the lens system110. More particularly, the correcting section 140 can restore the imageof the subject to a clear image by performing deconvolution with the useof an inverse filter designed to correct the optical response of thelens system 110, with reference to the amounts of light received by thepredetermined number of light receiving elements (for example, lightreceiving elements arranged in 3×3, 7×7 or the like).

As described above, the correcting section 140 corrects a plurality ofpixel values in accordance with two or more of the pixel values and theoptical transfer function, in order to reduce the influence, on thepixel values, of the spread of the light from the object point caused bythe lens system 110. Here, the correcting section 140 corrects the pixelvalues differently according to their color components, in accordancewith optical transfer functions of the lens system 110 for light of therespective color components. In other words, the correcting section 140can appropriately correct influence of spread of light, which may differdepending on different optical transfer functions of differentwavelengths.

FIG. 7 illustrates an exemplary block configuration of the non-linearprocessing section 170. The non-linear processing section 170 includes acolor correction section 810, a γ correction section 820, a colorinterpolation section 830, a YC conversion section 840, a colordifference correction section 850, and a contour correction section 860.

The color correction section 810 obtains, from the correcting section140, pixel values that have been corrected by the correcting section140. The color correction section 810 performs gain correction and colorcorrection on the pixel values obtained from the correcting section 140by using matrix processing. For example, the color correction section810 performs gain adjustment on the pixel values obtained from thecorrecting section 140, which represent the intensity levels of the R, Gand B components.

For example, the color correction section 810 may multiply the pixelvalues of the respective color components by gain values individuallydetermined for the color components. As an alternative example, thecolor correction section 810 may convert the pixel values of therespective color components into values expressed as a sum of pixelvalues of the respective color components multiplied by predeterminedcoefficients individually determined for the color components. Forexample, the color correction section 810 converts a pixel value of theR component into a value expressed as u_(R)×R+u_(G)×G+u_(B)×B, where R,G and B respectively denote values of the R, G and B component. Thevalues of u_(R), u_(G) and u_(B) may be differently set depending on thecolor components of the pixel values to be output. In this manner, thecolor correction section 810 may correct colors based on matrixprocessing. In the above-described manner, the color correction section810 performs color balance correction on an image represented by thepixel values that have been corrected by the correcting section 140.

The pixel values that have been subjected to the color correction by thecolor correction section 810 are supplied to the γ correction section820. The γ correction section 820 performs γ correction on the pixelvalues supplied from the color correction section 810. The γ correctioncan also convert the pixel values into values that are non-linearlyrelated to the amounts of the received light. Here, the γ correction mayinvolve changing the dynamic range. Thus, the γ correction section 820may convert the corrected pixel values into pixel values having adifferent dynamic range.

The pixel values that have been subjected to the γ correction by the γcorrection section 820 are supplied to the color interpolation section830. The color interpolation section 830 performs a coinciding operationon the pixel values that have been corrected by the color correctionsection 810 and converted by the γ correction section 820. Specificallyspeaking, the color interpolation section 830 performs colorinterpolation, thereby determining pixel values of all the colorcomponents in association with the position of each light receivingelement. For example, in the case of the light receiving elementarrangement shown in FIG. 6, light of the G and B components is notreceived at the position of the light receiving element 620.Accordingly, no pixel values are determined for the G and B componentsin association with the position of the light receiving element 620.

Therefore, the color interpolation section 830 performs interpolationbased on pixel values associated with the positions in the vicinity ofthe position of the light receiving element 620 (for example, the pixelvalue of the G component associated with the position of the lightreceiving element 610 a and the pixel value of the G componentassociated with the position of the light receiving element 611 a), tocalculate a pixel value associated with the position of the lightreceiving element 620. The color interpolation section 830 can calculatea pixel value of the B component in a similar manner. In associationwith the remaining positions, the color interpolation section 830 cansimilarly calculate pixel values of color components the light of whichis not received.

In the above-described manner, the color interpolation section 830performs interpolation on pixel values that have been corrected by thecorrecting section 140, by using the pixel values that have beencorrected. As previously described, the correcting section 140 correctsa plurality of pixel values differently depending on their colorcomponents, based on the optical transfer functions of the lens system110 for light of the individual color components. With such aconfiguration, the image capturing apparatus 100 can correct influenceon pixel values that may differ depending on different optical transferfunctions for different wavelengths, before the color interpolationsection 830 performs color interpolation.

The YC conversion section 840 calculates a luminance signal and a colordifference signal based on the R, G and B values obtained as a result ofthe interpolation performed by the color interpolation section 830. Theluminance signal calculated by the YC conversion section 840 is suppliedto the contour correction section 860 so that the contour correctionsection 860 performs contour correction on the luminance signal. Here,the operations performed by the contour correction section 860 caninclude edge enhancement. As stated, the contour correction section 860subjects an image represented by the pixel values that have beencorrected by the correcting section 140 to spatial frequency processingthat modulates the spatial frequency components of the image. On theother hand, the color difference signal is supplied to the colordifference correction section 850, so that the color differencecorrection section 850 performs color difference correction, such astonality correction, on the color different signal. Here, the colordifference correction performed by the color difference correctionsection 850 can include color enhancement.

As described above, the non-linear processing section 170 converts thepixel values into values that are non-linearly related to the amounts ofthe received light. The correcting section 140 can perform correctionwith the use of an inverse filter based on an optical transfer functionand the like before the non-linear processing section 170 performsnon-linear processing, that is to say, when the pixel values are stilllinearly related to the amounts of the received light. As a consequence,the image capturing apparatus 100 can restore an image of a subject moreaccurately.

FIG. 8 illustrates exemplary data stored on the condition storingsection 180 by using a table. The condition storing section 180 stores arange for the distance between the lens system 110 and a subject(DISTANCE D1 to DISTANCE D2), a range for the luminance of the subject(LUMINANCE I1 to LUMINANCE I2), a shape characteristic amount that is acharacteristic amount of the shape of the subject, and a colorcharacteristic amount that is a characteristic amount of the color ofthe subject. Here, the condition storing section 180 may store aplurality of shape characteristic amounts and a plurality of colorcharacteristic amounts. A color characteristic amount used to detect abarcode region can be exemplified by a ratio among white, black and grayvalues, and a shape characteristic amount used to detect atwo-dimensional barcode region can be exemplified by a lattice-liketexture pattern. Here, even if an image includes a blurry sectioncreated by the lens system 110, sufficient texture information can beextracted as long as the blurry section corresponds only to a fewpixels.

The region identifying section 160 identifies a partial region includinga subject satisfying a condition stored on the condition storing section180. Specifically speaking, the region identifying section 160identifies a partial region including a subject positioned at a distancethat falls within the range of DISTANCE D1 to DISTANCE D2, a subjectwhose luminance falls within the range of LUMINANCE I1 to LUMINANCE I2,a subject having the above shape characteristic amount or a subjecthaving the above color characteristic amount.

FIG. 9 illustrates exemplary partial regions identified by the regionidentifying section 160. It is assumed that the region identifyingsection 160 identifies partial regions 910 and 920 in an image 900 aspartial regions satisfying a condition stored on the condition storingsection 180. In this case, the correcting section 140 corrects thepartial regions 910 and 920 identified by the region identifying section160, in accordance with the optical characteristics of the lens system110, which are indicated by optical transfer functions for therespective partial regions. With such a configuration, even whendifferent optical transfer function are associated with different imageheights, the correcting section 140 can perform appropriate correctionaccording to image heights.

Here, the distance range of DISTANCE D1 to DISTANCE D2, which is storedon the condition storing section 180, is defined as follows. When thedistance from the lens system 110 to a given object point falls withinthe distance range of DISTANCE D1 to DISTANCE D2, the lens system 110may have a substantially constant optical transfer function for lightfrom the given object point, as described above. In this case, thecorrecting section 140 corrects a partial region of a substantiallyconstant optical transfer function, but does not correct other partialregions. In this manner, the image capturing apparatus 100 can preventartifacts from being generated because of correction that is performedby using an inverse filter designed for optical response different fromactual optical response.

Similar effects as above can be produced when the correcting section 140is configured to correct a partial region whose luminance falls withinthe range of LUMINANCE I1 to LUMINANCE I2. This configuration isparticularly advantageous when the image capturing apparatus 100captures an image of a subject in the vicinity thereof underillumination light, for example, when the image capturing apparatus 100is an image capturing device used in an endoscope system. Also, beingconfigured to correct a partial region having a shape characteristicamount or color characteristic amount that is stored on the conditionstoring section 180, the correcting section 140 can correct a partialregion showing a subject desired to be observed. Since the correctingsection 140 is configured to correct particular partial regions and notto correct other partial regions, the image capturing apparatus 100 canshorten a time period required for computation relating to thecorrection.

FIG. 10 illustrates diffraction limited MTF of the lens system 110. Aline 1000 indicates diffraction limited MTF characteristics. Here,correction of optical response performed by the correcting section 140by using an inverse filter or the like as described above is equivalentto bringing the MTF characteristics of the entire system including thelens system 110 and the correction by the correcting section 140 closerto the diffraction limited MTF characteristics.

FIG. 11 illustrates MTF characteristics obtained as a result ofcorrection by the correcting section 140. A line 1100 indicates MTFcharacteristics of the entire system resulting from correction of animage performed by the correcting section 140 using a certain inversefilter. As seen from FIG. 11, the MTF characteristics of the entiresystem are displaced from the diffraction limited MTF characteristics(indicated by a dotted line 1000). This displacement may be generatedwhen the correcting section 140 performs the correction by using aninverse filter designed for an optical transfer function different froman actual optical transfer function. When such displacement is generatedin a spatial frequency range to which human eyes are highly sensitive, acorrected image is unpleasant for human eyes.

For this reason, the region identifying section 160 identifies a partialregion in which the MTF characteristics are displaced from thediffraction limited MTF characteristics in a particular spatialfrequency range. For example, the region identifying section 160 mayidentify a partial region in which an artifact is generated, in an imageresulting from the correction by the correcting section 140. In order toidentify a partial region with an image pattern caused by the opticaltransfer function varying depending on image heights, the regionidentifying section 160 can identify such a partial region withreference to an optical transfer function of each partial region and again for each frequency range generated by the inverse filter. Thecorrection control section 175 then prohibits the correcting section 140from correcting the partial region identified by the region identifyingsection 160, or reduces a gain in the particular frequency range in thepartial region identified by the region identifying section 160. In theabove-described manner, the image capturing apparatus 100 can suppressartifacts that may be generated by the correction performed by thecorrecting section 140.

FIG. 12 shows an example of a plurality of image regions in a finalimage. The image region A is a central image region in the capturedimage, and image regions B to I are the image regions surrounding theimage region A. The subject near the optical axis of the lens system 110is captured in the image region A. The condition storing section 180stores, for each image region A to I, conditions relating to a distancerange of a subject captured in each region. The parameter storingsection 185 stores, for each image region image A to I, a correctionparameter that is used by the correcting section 140 when correctingeach image region.

FIG. 13 schematically shows an example of distance ranges indicatingpositions where a subject exists whose image can be corrected by thecorrecting section 140. When the distance from the lens system 110 isrepresented by z, the condition storing section 180 stores, as acondition for identifying the image region A as the partial region to becorrected, a condition indicating that the distance from the lens system110 to each subject is between z1 and z4. Furthermore, the conditionstoring section 180 stores, as a condition for identifying the imageregions B to I as the partial regions to be corrected, a conditionindicating that the distance from the lens system 110 to each subject isbetween z1 and z3 or between z2 and z4.

The region identifying section 160 determines, for each image region,whether the distance to each subject being captured is within thedistance range stored by the condition storing section 180 inassociation with the image region. The region identifying section 160then identifies the partial regions to be corrected by the correctingsection 140 as the image regions in which the distance to each subjectis within the distance range.

In this way, the condition storing section 180 stores a conditionrelating to the distance range for each image region. The regionidentifying section 160 identifies, for each image region, partialregions that fulfill the condition stored by the condition storingsection 180 for the image region.

The parameter storing section 185 stores, for each image region A to I,a correction parameter in association with a range of distances to thesubjects being captured in the image region. The correcting section 140corrects the image of each image region identified by the regionidentifying section 160, using the correction parameter stored by theparameter storing section 185 in association with the range of distancesto the subjects being captured.

FIG. 14 shows an exemplary table of information stored by the conditionstoring section 180 and the parameter storing section 185. For ease ofexplanation, the following description refers to the distance between z0and z1 as “short range,” the distance between z1 and z2 as “mid range,”and the distance between z2 and z3 as “long range.”

The condition storing section 180 stores, as the distance range to becorrected for the image region A, all combinations of the short range,the mid range, and the long range. The condition storing section 180stores, as the distance range to be corrected for the image region B,the short range, the mid range, the long range, a combination of theshort and mid ranges, and a combination of the mid and long ranges. Inthe same way, the condition storing section 180 stores, as the distancerange to be corrected for the image regions C to I, the short range, themid range, the long range, a combination of the short and mid ranges,and a combination of the mid and long ranges.

The parameter storing section 185 stores, for the image region A,correction parameters A1 to A6 in association with each of the possiblecombinations of the short, mid, and long ranges indicating the distanceranges to be corrected. For the image region B, the parameter storingsection 185 stores correction parameters B1 to B5 in association witheach of the short, mid, and long ranges, the combination of the shortand mid ranges, and the combination of the mid and long rangesindicating the distance ranges to be corrected. In the same way, foreach of the image regions C to I, the parameter storing section 185stores 5 correction parameters in association with the short, mid, andlong ranges, the combination of the short and mid ranges, and thecombination of the mid and long ranges indicating the distance ranges tobe corrected.

FIG. 15 shows examples of spatial frequency dependencies of MTFs. TheMTF 1501 represents an MTF for light that focuses at a prescribedposition on an image surface at a distance z1 from the lens system 110.The MTF 1503 represents an MTF for light that focuses at the prescribedposition on an image surface at a distance z2 from the lens system 110.The MTF 1502 represents an MTF for light that focuses at the prescribedposition on an image surface at a distance between z1 and z2 from thelens system 110.

As shown in FIG. 15, each MTF is substantially the same in the spatialfrequency band from DC to the spatial frequency f1. When the MTFs forthe light focusing at an image region near the prescribed position aresubstantially the same in the distance range from z1 to z2, the image ofa subject existing between z1 and z2 can be restored as a clear image bya restoration filter that is the same over the spatial frequency bandfrom DC to the spatial frequency f1. In this case, the restorationintensity of the restoration filter in a spatial frequency band higherthan the spatial frequency f1 should be set to substantially zero or toa value such that a difference in relation to an equivalent MTF afterrestoration is small enough to be ignored. When the correcting section140 performs the restoration using such a restoration filter, anequivalent restored MTF can be very near the MTF at an analytical limitin the spatial frequency band from DC to the spatial frequency f1.Furthermore, since the difference relative to a restored equivalent MTFis small enough to be ignored in the spatial frequency band higher thanthe spatial frequency f1, the artifacts caused by the restorationprocess can sometimes be suppressed.

The above describes performing the restoration using the same filter forthe image of each subject in the short range. In the same way, a spatialfrequency range in which the same filter can be used to restore a clearimage is determined for each of the mid range, the long range, thecombination of the short and mid ranges, the combination of the mid andlong ranges, and the combination of the short, mid, and long ranges.Accordingly, the parameter storing section 185 may store, in associationwith each of the distance ranges, a restoration filter that restoressubject images in a spatial frequency region having a substantiallyuniform optical transfer function. The parameter storing section 185 maystore these restoration filters for each of the image regions. Thecorrecting section 140 restores each of the image regions A to I usingthe restoration filters stored by the parameter storing section 185 inassociation with range of distances to the subjects being captured inthe image region.

In this way, the parameter storing section 185 stores correctionparameters that correct the images in spatial frequency regions in whichthe optical transfer function is substantially uniform over each of aplurality of different distance ranges, according to the opticaltransfer function associated with each distance range. The correctingsection 140 corrects the image of each partial region identified by theregion identifying section 160, using the correction parameters storedby the parameter storing section 185 in association with the range ofdistances to the subjects being captured in the partial region. Thiscorrection can achieve subject images that are free of artifacts.

FIG. 16 shows an exemplary captured image. As shown in FIG. 16, theimage regions A and D in the captured image mainly include an image of asubject s1. The image region B mainly includes an image of a subject s2and a portion of a subject s3. The image region E includes an image of aportion of a subject s4. The image region F includes an image of aportion of the subject s3 and an image of a portion of the subject s4.

FIG. 17 shows a positional relation between the image capturingapparatus 100 and the subjects s1 to s4 included in the captured image900, along with a face angle of the image capturing apparatus 100. Asshown in FIG. 17, the subject s1 and the subject s4 are in the shortrange distance, the subject s2 is in the mid range distance, and thesubject s3 is in the long range distance.

The majority of the image region A and the image region D is occupied bythe subject s1 in the short range distance. Accordingly, the regionidentifying section 160 identifies the image regions A and D as partialregions to be corrected by the correcting section 140. The correctingsection 140 determines the correction parameters for correcting theimage regions A and D to be (i) the short range filter A1 stored by theparameter storing section 185 in association with the short rangedistance and the image region A and (ii) the short range filter storedby the parameter storing section 185 in association with the short rangedistance and the image region D, respectively.

The image region B is occupied by the subjects s2 and s3, which are inthe combination of the mid range and the long range distances.Accordingly, the region identifying section 160 identifies the imageregion B as the partial region to be corrected by the correcting section140. The correcting section 140 determines the correction parameters forcorrecting the image region B to be the mid and long range filter B5corresponding to the combination of the mid and long ranges in which thesubjects s2 and s3 are present.

The image region F includes images of the subjects s3 and s4. Thedistance range of the subjects being captured in the image region Fspans from short range to long range. As described above, the distancerange spanning from short range to long range does not fulfill thecondition stored by the condition storing section 180 in associationwith the image region F. Accordingly, the image region F is notidentified by the region identifying section 160 as a partial region tobe corrected, and therefore the correcting section 140 does not applythe correction process to the image region F.

The image of the subject s4 is included in the image region E. Since theimage region F is not identified as a partial region to be corrected,the region identifying section 160 also does not identify the imageregion E that contains the same subject s4 as a partial region to becorrected. Therefore, even when a subject included in an image regionthat is not identified as a partial region to be corrected by thecorrecting section 140 is included in a different image region, theregion identifying section 160 need not identify the other image regionas a partial region to be corrected by the correcting section 140. As aresult, there is a decreased chance of a corrected region and anuncorrected region being mixed for images of the same subject.

The region identifying section 160 may identify whether certain imagesare of the same subject by determining whether the images have the samecolor distributions. In this way, the region identifying section 160 candetermine the subjects are the same from even a blurred subject image.

The image region C, in which there is only a subject at short range, isidentified by the region identifying section 160 as a partial region tobe corrected and is corrected by the correcting section 140 using theshort range filter. The image regions G, H, and I, in which there isonly a subject at long range, are identified by the region identifyingsection 160 as partial regions to be corrected and are corrected by thecorrecting section 140 using the long range filter.

As described above, the condition storing section 180 stores conditionsrelating to the distance range from the lens system 110 to the subjectsbeing captured in each image region. The region identifying section 160then identifies partial regions in which the distance range from thelens system 110 to the subjects being captured in each image regionfulfills the condition relating to the corresponding distance rangestored by the condition storing section 180. If the distances tosubjects being captured span a wide distance range, restoration usingthe same restoration filter might cause an artifact in the image.However, the image capturing apparatus 100 can often prevent artifactformation since the partial regions that fulfill the conditionsconcerning the distance range stored by the condition storing section180 are identified as the image regions to be restored.

FIG. 18 illustrates an exemplary hardware configuration of a computer1500 functioning as the image capturing apparatus 100. The computer 1500is constituted by a CPU surrounding section, an input/output (I/O)section and a legacy I/O section. The CPU surrounding section includes aCPU 1505, a RAM 1520, a graphic controller 1575, and a display device1580 which are connected to each other by means of a host controller1582. The I/O section includes a communication interface 1530, a harddisk drive 1540, and a CD-ROM drive 1560 which are connected to the hostcontroller 1582 by means of an I/O controller 1584. The legacy I/Osection includes a ROM 1510, a flexible disk drive 1550, and an I/O chip1570 which are connected to the I/O controller 1584.

The host controller 1582 connects the RAM 1520 with the CPU 1505 andgraphic controller 1575 which access the RAM 1520 at a high transferrate. The CPU 1505 operates in accordance with programs stored on theROM 1510 and RAM 1520, to control the constituents. The graphiccontroller 1575 obtains image data which is generated by the CPU 1505 orthe like on a frame buffer provided within the RAM 1520, and causes thedisplay device 1580 to display the obtained image data. Alternatively,the graphic controller 1575 may include therein a frame buffer forstoring thereon image data generated by the CPU 1505 or the like.

The I/O controller 1584 connects, to the host controller 1582, the harddisk drive 1540, communication interface 1530 and CD-ROM drive 1560which are I/O devices operating at a relatively high rate. The hard diskdrive 1540 stores thereon programs and data to be used by the CPU 1505.The communication interface 1530 couples to the network communicationapparatus 1598, to transmit/receive programs or data. The CD-ROM drive1560 reads programs or data from a CD-ROM 1595, and supplies the readprograms or data to the hard disk drive 1540 and communication interface1530 via the RAM 1520.

The I/O controller 1584 is also connected to the ROM 1510, flexible diskdrive 1550 and I/O chip 1570 which are I/O devices operating at arelatively low rate. The ROM 1510 stores thereon a boot program executedby the computer 1500 at the start up, programs dependent on the hardwareof the computer 1500 and the like. The flexible disk drive 1550 readsprograms or data from a flexible disk 1590, and supplies the readprograms or data to the hard disk drive 1540 and communication interface1530 via the RAM 1520. The I/O chip 1570 is used to connect a variety ofI/O devices such as the flexible disk drive 1550 via, for example, aparallel port, a serial port, a keyboard port, a mouse port or the like.

The program to be executed by the CPU 1505 is provided by a user in thestate of being stored on a recording medium such as the flexible disk1590, the CD-ROM 1595, and an IC card. The program may be stored on therecording medium in the state of being compressed or not beingcompressed. The program is installed from the recording medium onto thehard disk drive 1540, read by the RAM 1520, and executed by the CPU1505. The program executed by the CPU 1505 causes the computer 1500 tofunction as the A/D converting section 125, the linear processingsection 130, the correcting section 140, the non-linear processingsection 170, the output section 150, the region identifying section 160,the distance obtaining section 165, the condition storing section 180,the parameter storing section 185, and the correction control section175 described with reference to FIGS. 1 to 17.

The program mentioned above may be stored on an external recordingmedium. The recording medium is, for example, an optical recordingmedium such as DVD and PD, a magnet-optical recording medium such as MD,a tape medium, a semiconductor memory such as an IC card and the like,in addition to the flexible disk 1590 and CD-ROM 1595. The recordingmedium may be a storage device such as a hard disk or RAM which isprovided in a server system connected to a dedicated communicationnetwork or the Internet, and the program may be provided to the computer1500 via the network. In this way, the computer 1500 is controlled bythe program to function as the image capturing apparatus 100.

Although some aspects of the present invention have been described byway of exemplary embodiments, it should be understood that those skilledin the art might make many changes and substitutions without departingfrom the spirit and the scope of the present invention which is definedonly by the appended claims.

The claims, specification and drawings describe the processes of anapparatus, a system, a program and a method by using the terms such asoperations, procedures, steps and stages. When a reference is made tothe execution order of the processes, wording such as “before” or “priorto” is not explicitly used. The processes may be performed in any orderunless an output of a particular process is used by the followingprocess. In the claims, specification and drawings, a flow of operationsmay be explained by using the terms such as “first” and “next” for thesake of convenience. This, however, does not necessarily indicate thatthe operations should be performed in the explained order.

1. An image processing apparatus, comprising: a region identifyingsection that identifies a partial region that fulfills a presetcondition in a main image captured through an optical system in which anoptical transfer function relating to light from an object point issubstantially uniform regardless of a distance to the object point; anda correcting section that corrects an image of the partial regionidentified by the region identifying section, according to the opticaltransfer function of the optical system; and further comprising acondition storing section that stores the condition to be fulfilled bythe partial region corrected by the correcting section, wherein theregion identifying section identifies a partial region of the main imagethat fulfills the condition stored by the condition storing section,wherein the condition storing section stores a condition concerning adistance to a subject, and the region identifying section identifies apartial region in which is captured a subject positioned at a distancethat fulfills the condition stored by the condition storing section,wherein the condition storing section stores a range of distance fromthe optical system over which the optical transfer function issubstantially uniform, and the region identifying section identifies apartial region in which is captured a subject positioned within therange of distance stored by the condition storing section.
 2. The imageprocessing apparatus according to claim 1, further comprising a distanceobtaining section that obtains a distance from the optical system to asubject captured in the main image, wherein the region identifyingsection identifies a partial region in which the distance obtained bythe distance obtaining section for the subject being captured is withinthe distance range stored by the condition storing section.
 3. The imageprocessing apparatus according to claim 1, wherein the condition storingsection stores a condition concerning brightness of the image whenillumination light illuminates a subject positioned within a range ofdistance from the optical system to the object point in which theoptical transfer function is substantially uniform, and the regionidentifying section identifies, in the image of the subject illuminatedwith the illumination light, a partial region whose brightness fulfillsthe condition concerning the brightness stored by the condition storingsection.
 4. An image processing apparatus, comprising: a regionidentifying section that identifies a partial region that fulfills apreset condition in a main image captured through an optical system inwhich an optical transfer function relating to light from an objectpoint is substantially uniform regardless of a distance to the objectpoint; and a correcting section that corrects an image of the partialregion identified by the region identifying section, according to theoptical transfer function of the optical system; and further comprisinga condition storing section that stores the condition to be fulfilled bythe partial region corrected by the correcting section, wherein theregion identifying section identifies a partial region of the main imagethat fulfills the condition stored by the condition storing section,wherein the condition storing section stores a condition concerning adistance to a subject, and the region identifying section identifies apartial region in which is captured a subject positioned at a distancethat fulfills the condition stored by the condition storing section,wherein the condition storing section stores a condition concerning arange of distance from the optical system to each of a plurality ofsubjects captured in an image region, and the region identifying sectionidentifies a partial region in which each of the plurality of subjectscaptured in the image region are positioned within a range of distancefrom the optical system that fulfills the condition concerning the rangeof distance stored by the condition storing section.
 5. The imageprocessing apparatus according to claim 4, wherein the condition storingsection stores the condition concerning the range of distance for eachof a plurality of image regions, and the region identifying sectionidentifies, in each image region, a partial region that fulfills thecondition stored by the condition storing section for the correspondingimage region.
 6. The image processing apparatus according to claim 4,further comprising a parameter storing section that stores, inassociation with each of a plurality of distance ranges, a correctionparameter corresponding to the optical transfer function over thedistance range, wherein the correcting section corrects the image of thepartial region identified by the region identifying section using thecorrection parameter stored by the parameter storing section inassociation with the range of distances to each subject captured in thepartial region.
 7. The image processing apparatus according to claim 6,wherein the parameter storing section stores, in association with eachof a plurality of distance ranges, a correction parameter for correctingan image of a partial region in a spatial frequency region in which theoptical transfer function is substantially uniform over the distancerange, according to the optical transfer function, and the correctingsection corrects the image of the partial region identified by theregion identifying section using the correction parameter stored by theparameter storing section in association with the range of distance toeach subject captured in the partial region.
 8. An image processingmethod, comprising: identifying a partial region that fulfills a presetcondition in a main image captured through an optical system in which anoptical transfer function relating to light from an object point issubstantially uniform regardless of a distance to the object point;correcting an image of the identified partial region according to theoptical transfer function for the partial region of the optical systemstoring the condition to be fulfilled by the partial region corrected bythe correcting section, wherein the region identifying step identifies apartial region of the main image that fulfills the condition stored bythe condition storing step, wherein the condition storing step stores acondition concerning a distance to a subject, and the region identifyingstep identifies a partial region in which is captured a subjectpositioned at a distance that fulfills the condition stored by thecondition storing step, wherein the condition storing step stores arange of distance from the optical system over which the opticaltransfer function is substantially uniform, and the region identifyingstep identifies a partial region in which is captured a subjectpositioned within the range of distance stored by the condition storingstep.
 9. A computer readable medium storing thereon a program used by animage processing apparatus, the program causing a computer to functionas: a region identifying section that identifies a partial region thatfulfills a preset condition in a main image captured through an opticalsystem in which an optical transfer function relating to light from anobject point is substantially uniform regardless of a distance to theobject point; a correcting section that corrects an image of the partialregion identified by the region identifying section, according to theoptical transfer function for the partial region of the optical system;further comprising a condition storing section that stores the conditionto be fulfilled by the partial region corrected by the correctingsection, wherein the region identifying section identifies a partialregion of the main image that fulfills the condition stored by thecondition storing section, wherein the condition storing section storesa condition concerning a distance to a subject, and the regionidentifying section identifies a partial region in which is captured asubject positioned at a distance that fulfills the condition stored bythe condition storing section, wherein the condition storing sectionstores a range of distance from the optical system over which theoptical transfer function is substantially uniform, and the regionidentifying section identifies a partial region in which is captured asubject positioned within the range of distance stored by the conditionstoring section.
 10. An image processing apparatus, comprising: acorrecting section that corrects an image captured through an opticalsystem in which an optical transfer function relating to light from anobject point is substantially uniform regardless of a distance to theobject point, according to the optical transfer function of the opticalsystem; a region identifying section that identifies, in the imagecorrected by the correcting section, an overcorrected partial region inwhich an optical response of the optical system is overcorrected; and acorrection control section that suppresses intensity of the correctionby the correcting section in the overcorrected partial region identifiedby the region identifying section.
 11. The image processing apparatusaccording to claim 10, wherein the region identifying sectionidentifies, in the image corrected by the correcting section, anovercorrected partial region having a frequency region in which anoptical response of the optical system is corrected to be greater than apreset value.
 12. An image processing method, comprising: correcting animage captured through an optical system in which an optical transferfunction relating to light from an object point is substantially uniformregardless of a distance to the object point, according to the opticaltransfer function of the optical system; identifying, in the correctedimage, an overcorrected partial region in which an optical response ofthe optical system is overcorrected; and controlling intensity of thecorrection in the identified overcorrected partial region.
 13. Acomputer readable medium storing thereon a program used by an imageprocessing apparatus, the program causing a computer to function as: acorrecting section that corrects an image captured through an opticalsystem in which an optical transfer function relating to light from anobject point is substantially uniform regardless of a distance to theobject point, according to the optical transfer function of the opticalsystem; a region identifying section that identifies, in the imagecorrected by the correcting section, an overcorrected partial region inwhich an optical response of the optical system is overcorrected; and acorrection control section that suppresses intensity of the correctionby the correcting section in the overcorrected partial region identifiedby the region identifying section.
 14. An image processing method,comprising: identifying a partial region that fulfills a presetcondition in a main image captured through an optical system in which anoptical transfer function relating to light from an object point issubstantially uniform regardless of a distance to the object point; andcorrecting an image of the identified partial region according to theoptical transfer function for the partial region of the optical system;storing the condition to be fulfilled by the partial region corrected bythe correcting step, wherein the region identifying step identifies apartial region of the main image that fulfills the condition stored bythe condition storing step, wherein the condition storing step stores acondition concerning a distance to a subject, and the region identifyingstep identifies a partial region in which is captured a subjectpositioned at a distance that fulfills the condition stored by thecondition storing step, wherein the condition storing step stores acondition concerning a range of distance from the optical system to eachof a plurality of subjects captured in an image region, and the regionidentifying step identifies a partial region in which each of theplurality of subjects captured in the image region are positioned withina range of distance from the optical system that fulfills the conditionconcerning the range of distance stored by the condition storing step.15. A computer readable medium storing thereon a program used by animage processing apparatus, the program causing a computer to functionas: a region identifying section that identifies a partial region thatfulfills a preset condition in a main image captured through an opticalsystem in which an optical transfer function relating to light from anobject point is substantially uniform regardless of a distance to theobject point; and a correcting section that corrects an image of thepartial region identified by the region identifying section, accordingto the optical transfer function for the partial region of the opticalsystem; a condition storing section that stores the condition to befulfilled by the partial region corrected by the correcting section,wherein the region identifying section identifies a partial region ofthe main image that fulfills the condition stored by the conditionstoring section, wherein the condition storing section stores acondition concerning a distance to a subject, and the region identifyingsection identifies a partial region in which is captured a subjectpositioned at a distance that fulfills the condition stored by thecondition storing section, wherein the condition storing section storesa condition concerning a range of distance from the optical system toeach of a plurality of subjects captured in an image region, and theregion identifying section identifies a partial region in which each ofthe plurality of subjects captured in the image region are positionedwithin a range of distance from the optical system that fulfills thecondition concerning the range of distance stored by the conditionstoring section.